Process for producing a product high in titanium dioxide content



United States Patent 3,428,427 PROCESS FOR PRODUCING A PRODUCT HIGH IN TITANIUM DIOXIDE CONTENT Dusan Raicevic, Beloeil, Quebec, Canada, assignor to Quebec Iron and Titanium Corporation, New York, N.Y., a corporation of Canada No Drawing. Filed June 24, 1965, Ser. No. 466,859 U.S. Cl. 23--202 Claims Int. Cl. C01g 23/ 04 ABSTRACT OF THE DISCLOSURE This invention relates to a process for producing a product rich in titanium dioxide and relatively low in other materials from titaniferous material that is first leached with dilute sulfuric acid to produce a solid residue which is subsequently leached with a dilute aqueous alkaline solution to obtain a titanium dioxide product.

This invention relates to a process for producing a product high in titanium dioxide from iron-bearing titaniferous materials. More particularly, this invention relates to a process for producing a product that is rich in titanium dioxide, and that can be regarded as a synthetic rutile, from ilmenite ore, titanium-bearing slag, and the like.

The word ilmenite refers to a specific chemical, that is generally accepted as having the formula FeO.TiO' The precise form in which this mineral occurs varies from deposit to deposit. One of the important deposits is the Allard Lake deposit in Quebec, Canada. The ilmenite ore there is a mechanical mixture of ilmenite and hematite. Most ores of ilmenite are mixtures of ilmenite and hematite or magnetite.

The Allard Lake ore is smelted at Sorel, Quebec, by the Quebec Iron and Titanium Corporation, to produce iron and a slag that is rich in titanium dioxide. A general description of the smelting operation at Sorel and its products can be found in United States Patent 2,476,453, granted July 19, 1949.

Typical analyses of Allard Lake ilmenite ore, and of the slag that is produced therefrom, appear below in Table I.

TABLE I.TYPICAL ORES AND SLAGS In Table I, above, the term upgraded ilmenite ore is employed to refer to an ore thathas been upgraded by physical methods. Such methods would include conventional mineral dressing techniques. For example, to produce the upgraded ilmenite ore, whose analysis is presented in Table I, ore as received from the mine was crushed, ground, screened, and subjected to magnetic separation. These operations remove gangue materials.

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Leaching is a well-known technique for removing impurities from ilmenite ore and other titaniferous materials. It is possible to leach ilmenite ore with dilute sulfuric acid, such as, for example, sulfuric acid having a concentration from about 10% to about 60%, at temperatures from about 100 C. to about 250 C. or higher, and under pressures up to about 500 p.s.i., to produce a residue containing a high proportion of titanium dioxide and a much smaller proportion of impurities than would be found in the ore. The presence of a reducing agent, or the use of reducing conditions, has a beneficial effect upon the removal of impurities.

Attempts to leach titanium-bearing slag, in similar fashion, for the purpose of reducing impurities and upgrading the content of titanium dioxide, have encountered considerable difficulty. A practical and successful process for leaching slag is described in the copending patent application of Dr. Peter J. Ensio, Ser. No. 319,312, filed Oct. 28, 1963 now abandoned. The process that is described in this application recognizes that ferric ions are normally present in the leach liquor during the leaching of ilmenite ore, and that removal of the chromium and vanadium is therefore facilitated while removal of the iron is hindered; and that when leaching slag, however, ferric ions are absent, and trivalent titanium ions are normally present, so that the removal of iron is facilitated whereas the removal of chromium and vanadium is hindered.

The leaching technique described in the Ensio application is based upon the discovery that the presence of ferric ions in the leaching solution has a pronounced beneficial effect upon the removal of chromium and vanadium from the slag. The ferric ions can be introduced in various ways, such as, for example, by the addition of oxidants during leaching. Preferably, however, the ferric ions are provided by mixing the slag with an ilmenite ore, such as, for example, the Allard Lake ilmenite ore, that provides ferric ions.

Typical leaching conditions, according to the Ensio process, are those where the mixture of slag and ore comprises at least 50% to about 60% of slag; the acid strength is from about 35% up to about 60%; the temperature is at least 400 F.; the pressure is about 200 p.s.i. but may be higher, for example, up to about 500 p.s.i.; and the leaching time is at least about 2 hours The quality of the titanium dioxide residue that is obtained may be adjusted by controlling the leaching process variables, including acid concentration, temperature, pressure, time, and amount of excess acid employed. The term excess acid is used to refer to the amount of acid that is employed above that which is needed for the removal of iron, titanium, vanadium, calcium, magnesium, and other nontitaniferous impurities.

In a typical demonstration of leaching in accordance with the Ensio patent application, a mixture was prepared that contained 60% by weight of slag and 40% by weight of a beneficiated, 92 grade Allard Lake ore concentrate. (The grade number refers to the sum of the percentages of iron and titanium oxides present.) The slag contained titanium dioxide and 11% Ti O The slag and the ore each were ground, prior to leaching and mixing together, so that at least of the particles passed through a 325 mesh. A 45% fresh sulfuric acid was used for leaching, in excess, at a temperature of 400 F., under a pressure of about 200 p.s.i., for two hours.

After leaching, over-all titanium dioxide recovery in the residue was at least 98%. Repeated demonstrations of the process indicate that a product having the following specifications may be consistently produced:

Table II.Leached product specifications Chemical specifications: Percentage by weight Fe max 1.5 Cr O max 0.1 V 0.50.10 CaO-l-MgO max 0.5 Loss on ignition max 0.2 TiO (natural basis) 90-94 The leached product is in the form of a slurry containing solid particles all of which pass through a 20 mesh screen, and of which at most about 3% pass through a 200 mesh screen. The solid particles vary in color from light to dark brown, depending upon the particular reaction conditions to which the mixture has been subjected.

While leached products that fall within the specifications stated in Table II represent a substantial upgrading of the ilmenite ore, these products must compete technically with rutile that is obtained from natural rutile deposits of grades that are as high and sometimes higher than those of the leached products. Accordingly, there is a demand for a product having specifications higher than those that may be obtained by the best leaching techniques previously known.

One object of the present invention is to provide a practical process for treating an iron-bearing titaniferous material, to produce a product having a high content of titanium dioxide and relatively low contents of other materials.

A more specific object of the invention is to provide an improved leaching process for iron-bearing titaniferous material, that can produce products that are comparable to and competitive with products obtained from natural rutile deposits.

Another object of the invention is to provide a practical process that can be used with an ilmenite ore, for producing products that are comparable to and competitive with products obtained from natural rutile deposits and that are rich in titanium dioxide.

Another specific object of the invention is to provide a practical process for the production of a pigment material from an ilmenite ore.

A further specific object of the invention is to provide a practical process for the production, from an ilmenite ore, of a material that is rich in titanium dioxide and that is suitable for use as a feed material for the chlorination process for the production of titanium dioxide.

Still another specific object of the invention is to provide a practical process for the production, from ilmenite ore, of a material that is rich in titanium dioxide and that is usable as a coating for welding rods.

A more general object of the invention is to provide practical processes for producing products rich in titanium dioxide, and relatively low in other materials, including, for example, chromium, vanadium, iron, silica, and materials that are lost on ignition, from iron-bearing titaniferous materials such as, for example, ilmenite ore, upgraded ilmenite ore, and titanium-bearing slag.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

I have now found that a valuable product, that has a high content of titanium dioxide and a relatively low content of other, undesirable materials, may be produced by a process that comprises leaching an iron-bearing titaniferous material, in finely-divided form, with a dilute sulfuric acid solution, to obtain an iron-bearing solution and H a solid residue; separating the iron-bearing solution and the solid residue; and then leaching the solid residue with a dilute aqueous alkaline solution, to obtain a solid residue that is high in titanium dioxide content. As compared to products prepared by previously known processes, this product is relatively high in titanium dioxide content, and desirably low in its content of iron, chromium, vanadium, silica, and materials that are lost on ignition.

The product that is thus obtained can be further processed, if desired, by calcining, at an elevated temperature such as, for example, a temperature in the range between about 800 C. and 900 C., to produce a pigment material of a natural light beige color. Alternatively, the product may be mixed with a carbonaceous material and sintered at a temperature in the range from about 1000 C. to about 1400 C., to produce a synthetic rutile in porous form, that is suitable for use as a feed material for the chlorination process for the production of titanium dioxide, or that is suitable for the preparation of a coating for welding rods.

In one preferred embodiment of the process in accordance with this invention, the iron-bearing titanife-rous material is ground to an extremely small particle size, at which approximately of the particles will pass through a 325 mesh screen. The finely-divided material is then mixed with a dilute sulfuric acid, having a concentration in the range from about 10% to about 60%, and the mixture is heated in an autoclave at a temperature in the range from about C. to about 250 C., at a pressure up to about 300 p.s.i., for a sufliciently long time to permit substantially complete reaction between the sulfuric acid and the titaniferous material. The material is then discharged from the autoclave, and the liquid material is separated from the solid residue. The residue preferably is then washed, and then is subjected to a physical separation, preferably in a hydrocyclone, to separate the material under 325 mesh size from the larger material. The coarse material preferably is then subjected to a second leaching process with dilute sulfuric acid, to insure complete reaction. The fine material is passed on to the next step in the process.

The fine material is then further leached with a dilute aqueous alkaline solution, preferably a solution containing at least one member selected from the group consisting of alkali metal hydroxides and alkali metal carbonates. The term alkali metal is employed herein to describe the hydroxides and carbonates of potassium, sodium, lithium, and ammonia. This leaching step is preferably carried out with a solution of the character described having a concentration in the range from about 5% to about 25%, at atmospheric pressure, and at a temperature in the range from about 100 C. to about C., for a period of time in the range from about one and a half hours to about three hours. The solid material is then separated from the leaching liquid, and may be washed to remove any residual traces of the alkaline leach liquid.

The solid material may then .be further processed to produce a variety of products for desired applications. Calcining in the presence of a suitable modifier is the technique that is preferred for the production of materials for use as colored pigments. For the production of chlorination process feed materials or welding rod coatings, calcining is ordinarily preferred, after mixing with a carbonaceous material such as, for example, one of the soluble starches, a fuel oil, a low ash coke, sawdust, or some combination of these or equivalent materials. Ordinarily, such a mixture is pelletized for sintering, and water is used if necessary to assist in pelletizing.

In the calcining of these materials, among the many suitable modifiers that can be employed, to speed up the conversion of the leached residue to the form of rutile, antimony oxide and zinc oxide are two preferred materials. However, other modifiers may be employed, if desired, particularly if different colors are desired.

The invention is further explained in detail, below, by the description of several demonstrations thereof.

EXAMPLE 1 To demonstrate the invention on a small scale, 45 kgs. of a titanium-bearing slag, produced in electric furnace smelting of an ilmenite ore, and having a 70.3% content of titanium dioxide, was placed in a 50 gallon autoclave with 107.5 liters of 35% sulfuric acid. The mixture was then heated to a temperature of about 200 C. under autogenous pressure, for four hours.

The alkaline-leached residue, that had been treated with 25% potassium hydroxide, was calcined at 950 C. for two hours. The product was a synthetic rutile material that contained 96.7% titanium dioxide and about 0.2% iron, as determined by colorimetric analysis.

The materials were then removed from the autoclave, 5 The Process of the Present invention, as demonstrated settled, d d nt d, Th lid er l d several in this example, eiIected a substantial enrichment of the tim ith f h t t remove id l id, titanium dioxide content of the solid material, namely,

The acid-leached residue had the following partial to 967%; after calcining- Moreover, analysis: purines were sgbstantlall y reduced. 'In the cas elof s1l1ca Table III.Partial analysis of acidleached residue 2;} 5 232 1 22}; 263 2 3372 2? from an mma content Itemi0 Percentage by weghlt EXAMPLE 2 F 5 Another demonstration of the invention was made, folc o 0 0 lowing the same general procedure as was employed 1n 0 010 Example 1, but using sodium hydroxide as the alkaline L on i i 52 leaching material. The results are summarized below in The acid-leached residue, after washing, was separated Table in a hydrocyclone into an overflow fraction of fines, con- TABLE VI sisting essentially of materials having a particle size that 1504 Leach R s u n s a n t sp r Leach will pass through a 325 mesh screen, and into an under- Resume flow fraction of coarse materials, of larger size. The TiOQ, Fe, S102, T102, Fe, SiOr, coarse material was set aside for subsequent repetition of r percent percent percent percent percent percent th idq hi step 20 89.0 0.4 4.0 92.8 0.4 0.0

The comparative analyses of these two fractions appears in Table IV, below: The alkaline-leached residue above was mixed with substantially equal amounts, in admixture, of antimony TABLE tv-PARTIAL ANALYSES OF FRACTIONS oxide, Sb O and zinc oxide ZnO, in total amount of the Fines, Overflow, Coarse, Underflow, admixture of about 0.5%, as a modifier, and was then went Percent calcined in a rotary drum at temperatures in the range TiOz 89.0 67.8 from about 800 C. to about 900 C. The resulting prodfi 8:33 8:3 uct was suitable for use as pigment material and was V205 a 0.10 0.12 r characterized by a natural light beige color.

3:3? 3:3 Another portion of material, that had been acid-leached and alkaline-leached as just described, was mixed with The fines fraction was then divided into two parts. One Sawdust While the form 0f a pulp. The rnixture was part was mixed with a 10% Solution of pqtassium hydrox then filtered, with the observation that filtration was subide. The second part was mixed with a 25% solution of stahtlahy tathhtated by the PTeISehCF of the sawdhst- The potassium hydroxide. Both solutions were then heated molst mammal thfifl Pelletlled In a rotary drum, and in open reactors and were maintained at temperatures the pellets were then smtered at temperatures up to 1400 in the range from about 90 to about 105 C. fo two (3., for two hours. The synthetic rut le produced had a houm porous, spongy texture, and was eminently suitable for Thereafter, the solid residues were each r'epulped three use as a feed thaterfat t h Ehlonhatioh Process for times, then dried. The analyses of these fractions was as the manufacture of tltahlhm thoxtdefollows: EXAMPLES 38 TABLE V,-ANALYSES OF ALKALINEJJQAOHED Further to demonstrate the invention, the process was RESIDUES repeated, substantially in accordance with the procedures Material Leaohedwith Material Leeehedwith described in Example 1, but using as feed materials for Item g gggg gg g z gggg gf fi the process slag alone, a mixture of slag; and ilmenite ore, and ilmenite ore alone. The leached residues were calcined, following generally the procedure outlined in Example 2. :03 In the case of Examples 3, 5, and 7, the: alkaline leaching zggg 2' gstep was omitted, to provide comparative data to permit sio2 'IIIII 2:67 0192 an evaluation of the effectiveness of alkaline leaching.

The results are tabulated below in Table VII:

TABLE VII H2804, Leeched Residue NaOH Leached Residue Synthetic Material Rutile Product Leached 'IiOz, Fe, SiOz, TiOz, Fe, SiOz, Ti02. Fe,

percent percent percent percent percent percent persent percent Example 3 Slag Alone.-- 90.1 0.3 4. 0 Not Leached 94.2 0.3

Slag/ole 88.8 1.5 2.8 Not Leeched 92.6 1.55

. Ore Alone 85. 2 2. 7 4. 5 Not Leached 90.1 2.8

Example8 .410 85.2 2.7 4.5 88.0 2.7 93.4 3.0

The mixture of slag and ore in each case included parts slag to 30 parts of ore, by weight. 2 The acid leaching step was repeated twice, without hydrocyclone separation between the first and second acid leaching steps.

As the data in Table VII demonstrates, the process of the present invention is highly effective in producing a high quality synthetic rutile product that is unusually rich in its content of titanium dioxide, and unusually low in its content of iron and silica.

EXAMPLES 9-18 'Further to demonstrate the invention, the data from several additional performances of the process, using different alkaline leaching conditions, are summarized below in Table VIII, as follows:

TABLE VIII H1804, Pressure Leach Alkaline Atmospheric Leach Synthetic Rutile Feed Residue-Fines Residue Kind and Slag, Ore, TiOz, Fe, SiOi, percent TiOz, Fe, S101, TiOz, Fe, percent percent percent percent percent soln percent percent percent percent percent Example No.:

9 100 89.0 0.4 3. 91 10% KOH- 91. 9 0.4 2. 6 95. 7 0. 44 89.0 0.4 3. 91 25% K011..." 93. 3 0.4 1. 98. 0 0.45

89. 0 0. 4 4. 0 10% NaOH.. 92. 9 0. 4 1. 97. 2 0.4

90. l. 0.3 4. 0 25% NaOH 92. 9 0.3 0.8 96. 7 0. 3

89.0 0.4 4.0 25% NaOH 92.8 0.4 0.6 98.7 0.4

88.8 1. 5 2.8 NaOH 91.6 1.6 1.0 94. 7 1.6

88. 8 1. 5 2. 8 NaO H. 91. 2 1. 6 0. 9 96. 1 1.6

88. 8 1. 5 2. 8 25% NazCO 89.8 1. 6 2.1 93. 4 1. 6

85. 2 2. 7 4. 4% Nil 90. 1 3. 0

85.2 2. 7 4. 48 25% NaOH- 88.0 2. 7 1. 5 93. 4 3. 5

In the performance of the invention as summarized above in Table VIII, the acid leaching conditions were generally the same as those described previously, with the exception that in Examples 17 and 18, the acid leaching step was repeated twice on the same feed material, in view of the fact that ore was being used.

As the foregoing demonstrations of the invention amply demonstrate, the process of the present invention permits a significant increase in the titanium dioxide content of products, such as synthetic rutiles, that can be produced from ilmenite ores and titanium-bearing slags.

To carry out the acid leaching step, the use of pure acid is not necessary. Sulfuric acid waste acids from several industries, particularly from the manufacture of TiO pigments, can be used advantageously. A typical pigment plant waste acid may have the following analysis, for example:

Table IX.-Pigment plant waste acid analysis Item: Content, g.p.l. T10 6 CI'203 0.4 V 0 1.3 Ferrous iron 2.5 Sulfuric acid 300 From the economic standpoint, the process of the present invention presently has greatest attraction where the feed material is an ilmenite ore. However, for applications where the end product must have low contents of iron, chromium, vanadium, silica, and other gangue materials, technical considerations will require the selection of a slag-ilmenite ore mixture as the raw material for the process. Similarly, leaching 'with pigment plant waste acid is economically attractive where such acid is available at relatively low cost. Its performance is almost as good as that of fresh acid of equal strength. However, where the end product must meet high specifications, improved end product analyses can be obtained either by increasing the strength of the waste acid, either by evaporation or fortification, or by increasing the severity of the leaching conditions, or by using fresh acid.

In general, time and temperature in leaching have a common effect, such that longer times at lower temperatures are equivalent to shorter times at higher temperatures. This is true of both the acid and alkaline leaching operations.

An additional advantage of the present process is that the liquors from the acid and alkaline leaching operations can be used, partially to neutralize each other. This facilitates disposal of the liquid efl luent from the process.

While the invention has been disclosed herein by reference to the details of preferred embodiments thereof, it is to be understood that such disclosure is intended in an illustrative, rather than a limiting sense, and it is contemplated that various modifications will readily occur to those skilled in the art, within the spirit of the invention and the scope of the appended claims.

I claim:

1. A proces for leaching an iron-bearing titaniferous material that comprises:

leaching the material in finely divided form with a dilute sulfuric acid solution, to obtain an iron-bearing solution and a solid residue;

separating the iron-bearing solution and the solid residue, and

leaching the solid residue with a dilute aqueous alkaline solution, to obtain a solid residue that is high in TiO content.

2. A process in accordance with claim 1 wherein the acid leaching step is carried out with a sulfuric acid solution having a concentration in the range from about 10% to about 60%, at a temperature in the range from about C. to about 250 C., and under a pressure up to about 300 psi.

3. A process in accordance with claim 1 wherein the dilute aqueous alkaline solution is a solution containing at least one member selected from the group consisting of an alkali metal hydroxide and an alkali metal carbonate.

4. A process in accordance with claim 3 wherein the alkaline leach is conducted at an elevated temperature up to about C.

5. A process in accordance with claim 1 including the additional step of firing the solid residue from the alkaline leaching step at an elevated temperature in excess of 800 C. to reduce the moisture content of said residue.

6. A process in accordance with claim 1 including the additional step of mixing the solid residue from the alkaline leaching with a carbonaceous material, then sintering the mixture at a temperature of at least about 1000 C. to reduce the moisture content of said residue and to thereby produce a synthetic rutile product in porous form.

7. A process for leaching an iron-bearing titaniferous material that comprises:

leaching the material in a particle size at which at least 85% of the particles are minus 325 mesh, with a dilute sulfuric acid solution to obtain an iron-bearing solution and a solid residue;

separating the residue into a first fraction that is reacted sufliciently with the acid so that the iron content, expressed as metallic iron, has been reduced to a content of about less than 4% and 'to a second fraction that is not as completely reacted as the first fraction; and

leaching said first fraction with a dilute aqueous alkaline solution, to obtain a solid residue that is 'high in TiO content.

8. A process in accordance with claim 7 including the additional step of reprocessing the second fraction of the acid-leached residue through a second, similar acid leaching step, to react it more completely, then reprocessing it through a second, similar alkaline leaching step.

9. A process in accordance with claim 8 including the additional step of firing the solid residue from the acid leaching and alkaline leaching steps to reduce the moisture content of said residue.

References Cited UNITED STATES PATENTS 2,731,327 1/1956 Anderson et a1. 23-202 2,804,375 8/1957 Kamlet 23-20Z 2,875,107 2/1959 Daiger 23-202 XR 2,961,298 11/1960 Tikkanen 23-1202 3,001,854 9/ 1961 Kenworthy 23117 3,018,170 1/ 1962 Soloducha 23--202 XlR. 3,069,235 12/1962 Schecter et a1. 2'3-202 2,815,272 12/1957 Anmant et a1. 75--1 2,974,014 3/ 1961 Hoekje et a1. 751 XIR EDWARD STERN, Primary Examiner.

US. Cl. X.R. 

